It has been common practice in the past to mount and wire the power supply elements of a microwave oven individually in whatever space might be available adjacent the microwave oven cavity. Similar wiring techniques have been employed in the so-called "common cavity" ovens employing both a thermal heating element and source of microwave energy. This has not only made assembly difficult and relatively expensive, but cooling of the microwave elements has been difficult and haphazard, shielding has been imperfect, and servicing has been a problem particularly in the case of common cavity ovens where the oven forms part of a range which cannot be moved to a testing facility.
With the increasing popularity of microwave cooking, manufacturers of conventional thermal ranges, particularly electric ranges, have given thought to the addition of a microwave energy source to conventional range designs, simply by feeding microwave energy to an existing cavity, with suitable steps being taken to redesign the sealing structure for the purpose of containing the microwave radiation. However, where conventional wiring and mounting techniques are employed, shielding or containing of the microwave generator, power supply, and associated cooling system, becomes complex and costly, especially when the conventional range storage drawer feature is retained, to say nothing of the expense of "on site" repair should servicing subsequently become necessary.
Because of the complication and expense, manufacturers have been slow in attempts to convert conventional designs of thermal ranges to "common cavity" microwave usage, the complications being particularly severe in the case of ovens having high temperature self-cleaning capability. By way of example, such ovens require a slight flow of convected air normally obtained through a gap in the door gasket. A gap in the gasket cannot, of course, be tolerated in the case of a microwave oven which requires tight shielding of the electrical field in the cavity.